In a printing system, such as those employing laser printers, ink jet printers or large commercial size offset printers, data representing an image to be printed (from an application such as a word processor or graphics program) must be converted to a raster format for the print engine (the electronic circuitry controlling the mechanical printing hardware) of a printer. The raster-format print data instructs the print engine where to deposit marking agents such as, but not limited to, ink or toner that form individual picture elements of a printed page, onto the print media. The locations where toner droplets are to be placed onto a media are usually referred to as picture elements, pixels or “pels.”
Laser printers, ink jet printers and commercial offset printers, typically include a rendering system in the printer which accepts output from a content-generating program such as WORD®, Photoshop® and others and generates a data set that the printer can understand and from which a page can be printed. A rendering system includes a combination of hardware and software to accomplish the rendering task which is commonly referred to as raster image processing or “RIPping.”
Printing an image or page from a content-generating program or other source begins with the creation of a digital image data file, referred to as a “print job.” A printer driver is used to convert the digital image file into a page description language (PDL) file using well-known techniques in the art. The PDL file is transmitted to either a printer buffer or to a separate raster image processor and then to the printer.
Several operations are performed on the PDL file including, but not limited to: compression, decompression, color space conversion, half-toning and formatting. The various processing operations can be performed using software or hardware, including a suitably programmed processor within the printer or by an external raster image processor.
If raster image processing is performed within a printer, the printer formatter receives the receives the PDL file and RIPs (i.e., converts) it to a format acceptable to the print engine. In the case of a laser printer, a corresponding electronic image is formed on the photo conductor drum, which is subsequently transferred to the print media to form a printed hard copy output page. The printer formatter is designed to convert most PDL print jobs to a required format at a rate sufficiently high so as to allow the printer to run at a rated speed.
Complex print jobs, including those performed by large commercial-size printers, require significant processing time thereby reducing the rate at which data can be transferred to the print engine, resulting in reduced output page printing rates. In a commercial printing environment, where print production volume is of paramount importance, it is important to run a commercial printing press at its maximum capacity.
One approach to address the RIP bottle neck is to perform the RIP tasks at the host computer, the processors of which are typically much more robust than the processors within a printer. A problem with burdening a host processor with the task of RIPping a print job however is that the host processor thereafter suffers a performance degradation during the course of RIPping a print job.
For these and other reasons, there is a need for the present invention.